ENH: Re-implemented cmGeneratedFileStream to look like a real stream and replace the destination file atomically. This will avoid problems with the process being terminated while generating a file.

Source/cmGeneratedFileStream.h

@@ -9,8 +9,8 @@
   Copyright (c) 2002 Kitware, Inc., Insight Consortium.  All rights reserved.
   See Copyright.txt or http://www.cmake.org/HTML/Copyright.html for details.
 
-     This software is distributed WITHOUT ANY WARRANTY; without even 
-     the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR 
+     This software is distributed WITHOUT ANY WARRANTY; without even
+     the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
      PURPOSE.  See the above copyright notices for more information.
 
 =========================================================================*/
@@ -18,122 +18,65 @@
 #define cmGeneratedFileStream_h
 
 #include "cmStandardIncludes.h"
-#include "cmSystemTools.h"
+
+// This is the first base class of cmGeneratedFileStream.  It will be
+// created before and destroyed after the ofstream portion and can
+// therefore be used to manage the temporary file.
+class cmGeneratedFileStreamBase
+{
+protected:
+  // The constructor prepares the temporary output file.
+  cmGeneratedFileStreamBase(const char* name, bool copy_if_different);
+
+  // The destructor renames the temporary output file to the real name.
+  ~cmGeneratedFileStreamBase();
+
+  // Internal file replacement implementation.
+  int RenameFile(const char* oldname, const char* newname);
+
+  // The name of the final destination file for the output.
+  std::string m_Name;
+
+  // The name of the temporary file.
+  std::string m_TempName;
+
+  // Whether to do a copy-if-different.
+  bool m_CopyIfDifferent;
+
+  // Whether the destination file should be replaced.
+  bool m_Okay;
+};
 
 /** \class cmGeneratedFileStream
- * \brief Output stream for generated files that does copy-if-different.
+ * \brief Output stream for generated files.
  *
- * Many files generated by CMake don't change each time they are generated.
- * This class can be used in place of std::ofstream to open a file and
- * write output to it.  The class will automatically write output to a
- * temporary file and copy it over an existing file only if the generated
- * file has changed.
+ * File generation should be atomic so that if CMake is killed then a
+ * generated file is either the original version or the complete new
+ * version.  This stream is used to make sure file generation is
+ * atomic.  Optionally the output file is only replaced if its
+ * contents have changed to prevent the file modification time from
+ * being updated.
  */
-class cmGeneratedFileStream
+class cmGeneratedFileStream: private cmGeneratedFileStreamBase,
+                             public std::ofstream
 {
 public:
   /**
    * The constructor takes the name of the file to be generated.  It
-   * automatically generates a name for the temporary file.
+   * automatically generates a name for the temporary file.  The
+   * second argument specifies whether the copy-if-different check
+   * should be done.  If the file cannot be opened an error message is
+   * produced unless the third argument is set to true.
    */
-  cmGeneratedFileStream(const char* name):
-    m_Name(name),
-    m_TempName(m_Name+".tmp"),
-    m_Stream(m_TempName.c_str()),
-    m_Copied(false),
-    m_AlwaysCopy(false)
-    {}
-  
-  /**
-   * The destructor ensures that the file has been closed and copied if
-   * it has changed.
-   */
-  ~cmGeneratedFileStream() { this->DoCopy(); }
-  
-  /**
-   * Get the real output stream.
-   */
-  std::ostream& GetStream() { return m_Stream; }
-  
-  /**
-   * Allow a test for whether the file is open.
-   */
-  operator bool() { return m_Stream.good(); }
-  
-  /**
-   * Close the file stream.  This will cause the copy-if-different to the
-   * real file name to occur.
-   */
-  void close() { this->DoCopy(); }
-  /**
-   * If always copy is true, then copy the file all the time without
-   *  checking for differences.  The default is false.
-   */
-  bool SetAlwaysCopy(bool v) { m_AlwaysCopy = v; return v;}
-private:
-  /**
-   * The name of the real file where output will be copied if it has changed.
-   */
-  std::string m_Name;
-  
-  /**
-   * The name of the temporary file.
-   */
-  std::string m_TempName;
-  
-  /**
-   * The real output stream used to write to the file.
-   */
-  std::ofstream m_Stream;
-  
-  /**
-   * Whether the temporary file has already been copied to the real file.
-   */
-  bool m_Copied;
+  cmGeneratedFileStream(const char* name, bool copy_if_different,
+                        bool quiet = false);
 
   /**
-   *  If always copy is true, then copy the file all the time without
-   *  checking for differences.  The default is false.
+   * The destructor checks the stream status to be sure the temporary
+   * file was successfully written before allowing the original to be
+   * replaced.
    */
-  bool m_AlwaysCopy;
-  
-  /**
-   * Closes the temporary file and does the copy-if-different to the
-   * real file.
-   */
-  void DoCopy()
-    {
-    if(!m_Copied)
-      {
-      m_Stream.close();
-      if(m_AlwaysCopy)
-        {
-        cmSystemTools::cmCopyFile(m_TempName.c_str(), m_Name.c_str());
-        }
-      else
-        {
-        cmSystemTools::CopyFileIfDifferent(m_TempName.c_str(),
-                                           m_Name.c_str());
-        }
-      cmSystemTools::RemoveFile(m_TempName.c_str());
-      m_Copied = true;
-      }
-    }
+  ~cmGeneratedFileStream();
 };
 
-
-/**
- * Allow a cmGeneratedFileStream to be used just as a real std::ostream
- * would be.
- */
-template <class T>
-std::ostream& operator << (cmGeneratedFileStream& l, const T& r)
-{
-  std::ostream& os = l.GetStream();
-  os << r;
-  return os;
-}
-
-
-
 #endif